Novel contact structure

ABSTRACT

A semiconductor device includes: a fin structure disposed on a substrate; a gate feature that traverses the fin structure to overlay a central portion of the fin structure; a pair of source/drain features, along the fin structure, that are disposed at respective sides of the gate feature; and a plurality of contact structures that are formed of tungsten, wherein a gate electrode of the gate feature and the pair of source/drain features are each directly coupled to a respective one of the plurality of contact structures.

BACKGROUND

As integrated circuit (IC) scaling proceeds into the deep sub-nanometerregime, the number of transistors on high performance, high density ICsis in the tens of millions, in accordance with the historical trend ofMoore's Law. This has necessitated scaling down respectiveinterconnection structures of the IC accordingly. In particular,tungsten (W) has been used for the interconnection structures (e.g.,contact plugs, vias, and other interconnection lines, etc.) that arerelatively closer to respective transistors of the IC. This is partiallybecause copper (Cu), which is typically used for another major portionof the interconnection structures that are relatively farther from thetransistors, may “poison” the transistors. For brevity, such tungsteninterconnection structure are herein collectively referred to as“tungsten contacts.”

Such tungsten contacts are usually formed using fluorine-based (F-based)chemical vapor deposition (CVD) techniques to overlay an active featureof the transistor, which is typically formed of silicon, withtungsten-based material (e.g., tungsten atoms). In general, the F-basedCVD techniques inevitably induces fluoride atoms to attack the activefeature formed of silicon. In this regard, one or more barrier layersformed of titanium (Ti)-based and/or tantalum (Ta)-based materials oralloys (e.g., Ti, Ta, TiN, TaN, and combinations thereof), serving as afluoride barrier layer, are formed to cover the active feature prior toforming the tungsten contact.

As mentioned above, the interconnection structures, including thetungsten contacts, are scaled down in accordance with the Moore's Law.However, such fluoride barrier layers cannot be scaled down accordingly.Thus, existing tungsten contacts and the methods forming the same arenot entirely satisfactory.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that various features are not necessarily drawn to scale. In fact,the dimensions and geometries of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A and 1B illustrate a flow chart of an embodiment of a method toform a semiconductor device, in accordance with some embodiments.

FIGS. 2A, 3A, 4A, 5A, 6A, 7A, 8A, 9A, 10A, 11A, 12A, 13A, 14A, and 15Aillustrate perspective views of an exemplary semiconductor device, madeby the method of FIGS. 1A-1B, during various fabrication stages, inaccordance with some embodiments.

FIGS. 2B, 3B, 4B, 5B, 6B, 7B, 8B, 9B, 10B, 11B, 12B, 13B, 14B, and 15Billustrate corresponding cross-sectional views of FIGS. 2A, 3A, 4A, 5A,6A, 7A, 8A, 9A, 10A, 11A, 12A, 13A, 14A, and 15A taken along a firstdirection, in accordance with some embodiments.

FIGS. 14C and 15C illustrate corresponding cross-sectional views ofFIGS. 14A and 15A taken along a second direction, in accordance withsome embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following disclosure describes various exemplary embodiments forimplementing different features of the subject matter. Specific examplesof components and arrangements are described below to simplify thepresent disclosure. These are, of course, merely examples and are notintended to be limiting. For example, the formation of a first featureover or on a second feature in the description that follows may includeembodiments in which the first and second features are formed in directcontact, and may also include embodiments in which additional featuresmay be formed between the first and second features, such that the firstand second features may not be in direct contact. In addition, thepresent disclosure may repeat reference numerals and/or letters in thevarious examples. This repetition is for the purpose of simplicity andclarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure provides various embodiments of a contactstructure immediately adjacent (e.g., coupled) to a conductive featureof a semiconductor device. In some embodiments, such a contact structuredirectly contacts, at least part of, the conductive feature of thesemiconductor device (e.g., a gate feature, drain feature, or sourcefeature of a metal-oxide-semiconductor field-effect-transistor(MOSFET)). In some embodiments, such a contact structure may be atungsten contact. In some embodiments, the tungsten contact may beformed by a fluoride-free deposition technique, for example, afluoride-free chemical vapor deposition (CVD) technique. As such, whileforming the tungsten contact using the fluoride-free CVD technique tocontact the conductive feature of the semiconductor device, theabove-mentioned fluoride barrier layer is not needed, which mayadvantageously allow the tungsten contact to be scaled down morecompactly with the corresponding conductive feature of the semiconductordevice.

FIGS. 1A and 1B illustrate a flowchart of a method 100 to form asemiconductor device including one or more of the disclosed contactstructures, according to one or more embodiments of the presentdisclosure. It is noted that the method 100 is merely an example, and isnot intended to limit the present disclosure. In some embodiments, thesemiconductor device may include a FinFET. As employed by the presentdisclosure, the FinFET refers to any fin-based, multi-gate transistor.It is noted that the method of FIGS. 1A-1B does not produce a completedFinFET or semiconductor device. A completed FinFET may be fabricatedusing complementary metal-oxide-semiconductor (CMOS) technologyprocessing. Accordingly, it is understood that additional operations maybe provided before, during, and after the method 100 of FIGS. 1A-1B, andthat some other operations may only be briefly described herein.

In some embodiments, the method 100 starts with operation 102 in which asemiconductor substrate is provided. The method 100 continues tooperation 104 in which one or more fins are formed extending beyond amajor surface of the semiconductor substrate. The method 100 continuesto operation 106 in which a first dielectric material is deposited overthe semiconductor substrate to overlay the fin. The method 100 continuesto operation 108 in which a top surface of the fin is exposed. Themethod 100 continues to operation 110 in which an upper fin of the finis exposed. The method 100 continues to operation 112 in which an oxidelayer is formed over the exposed upper fin. The method 100 continues tooperation 114 in which a dummy gate stack is formed over respectivecentral portions of the oxide layer and the upper fin. The method 100continues to operation 116 in which source/drain (S/D) features arerespectively formed at sides of the dummy gate stack. The method 100continues to operation 118 in which a second dielectric layer is formedover the S/D features. The method 100 continues to operation 120 inwhich at least part of the dummy gate stack is removed. The method 100continues to optional operation 122 in which the oxide layer is removed.The method 100 continues to operation 124 in which a gate feature isformed over the central portion of upper fin. The method 100 continuesto operation 126 in which a third dielectric layer is formed over thegate feature and the second dielectric layer. The method 100 continuesto operation 128 in which the third dielectric layer is recessed toexpose respective top surfaces of the gate feature and the S/D features.The method 100 continues to operation 130 in which respective tungstencontacts are formed to directly contact the gate features and the S/Dfeatures.

In some embodiments, operations of the method 100 may be associated withperspective views of a semiconductor device 200 at various fabricationstages as shown in FIGS. 2A, 3A, 4A, 5A, 6A, 7A, 8A, 9A, 10A, 11A, 12A,13A, 14A, and 15A, respectively, and corresponding cross-sectionalviews, taken along a first direction, as shown in FIGS. 2B, 3B, 4B, 5B,6B, 7B, 8B, 9B, 10B, 11B, 12B, 13B, 14B, and 15B. Further, for purposeof clarity of illustration, with respect to the perspective views of thesemiconductor device 200 at the fabrication stages as shown in FIGS. 14Aand 15A, corresponding cross-sectional views of the semiconductor device200, taken along a second direction, are shown in FIGS. 14C and 15C,respectively. In some embodiments, the semiconductor device 200 may be aFinFET. The FinFET 200 may be included in a microprocessor, memory cell,and/or other integrated circuit (IC). FIGS. 2A through 14B aresimplified for a better understanding of the concepts of the presentdisclosure. For example, although the figures illustrate the FinFET 200,it is understood the IC may comprise a number of other devicescomprising resistors, capacitors, inductors, fuses, etc., which are notshown in FIGS. 2A through 14B, for purposes of clarity of illustration.

Corresponding to operation 102 of FIG. 1A, FIG. 2A is a perspective viewof the FinFET 200 including a semiconductor substrate 202, which isprovided at one of the various stages of fabrication, according to someembodiments, and FIG. 2B is a cross-sectional view of the FinFET 200taken along line a-a (along the X direction) of FIG. 2A. As shown, thesemiconductor substrate 202 is covered by a pad layer 204, a first masklayer 206, and a photo-sensitive layer 208 that is patterned with one ormore openings 210. The photo-sensitive layer 208 is patterned to formone or more fins of the FinFET 200, which will be discussed in thefollowing operations.

In some embodiments, the semiconductor substrate 202 comprises acrystalline silicon substrate (e.g., wafer). In some alternativeembodiments, the semiconductor substrate 202 may be made of some othersuitable elemental semiconductor, such as diamond or germanium; asuitable compound semiconductor, such as gallium arsenide, siliconcarbide, indium arsenide, or indium phosphide; or a suitable alloysemiconductor, such as silicon germanium carbide, gallium arsenicphosphide, or gallium indium phosphide. Further, the semiconductorsubstrate 202 may include an epitaxial layer (epi-layer), may bestrained for performance enhancement, and/or may include asilicon-on-insulator (SOI) structure.

In some embodiments, the pad layer 204 may be a thin film comprisingsilicon oxide formed, for example, using a thermal oxidation process.The pad layer 204 may act as an adhesion layer between the semiconductorsubstrate 202 and the first mask layer 206. The pad layer 204 may alsoact as an etch stop layer while etching the first mask layer 206. Insome embodiments, the first mask layer 206 is formed of silicon nitride(SiN), silicon carbon nitride (SCN), silicon oxide nitride (SON), or thelike, for example, using low-pressure chemical vapor deposition (LPCVD),plasma enhanced chemical vapor deposition (PECVD), or spin-on coating.The first mask layer 206 is used as a hard mask during subsequentphotolithography processes. The photo-sensitive layer 208 is formed onthe first mask layer 206, and then patterned thereby forming theopenings 210 in the photo-sensitive layer 208.

Corresponding to operation 104 of FIG. 1A, FIG. 3A is a perspective viewof the FinFET 200 including a fin 212, which is formed at one of thevarious stages of fabrication, according to some embodiments, and FIG.3B is a cross-sectional view of the FinFET 200 taken along line a-a(along the X direction) of FIG. 3A. It is noted that although only onefin 212 is shown in the illustrated embodiments of FIGS. 3A and 3B (andthe following figures), any desired number of fins may be formed on thesemiconductor substrate 202 using the photo-sensitive layer 208 (FIGS.2A and 2B) with an according pattern.

In some embodiments, the fin 212 is formed by at least some of thefollowing processes. The first mask layer 206 and pad layer 204 areetched through openings 210 (FIGS. 2A and 2B) to expose underlyingsemiconductor substrate 202. By using remaining pad layer 204 and thefirst mask layer 206, as shown in FIGS. 3A and 3B, the exposedsemiconductor substrate 202 is then etched to form trenches 213 so as tocause a major surface 203 of the semiconductor substrate 202 to beexposed. A portion of the semiconductor substrate 202 sandwiched betweenthe trenches 213 are thus formed as the fin 212. The fin 212 extendsupward from the major surface 203. The trenches 213 may be strips(viewed from the top of the FinFET 200) parallel to each other, andclosely spaced with respect to each other. After the fin 212 is formed,the photo-sensitive layer 208 (not shown in FIGS. 3A and 3B for purposesof clarity) is removed. Subsequently, a cleaning process may beperformed to remove a native oxide of the semiconductor substrate 202.The cleaning may be performed using diluted hydrofluoric (DHF) acid, orthe like.

Corresponding to operation 106 of FIG. 1A, FIG. 4A is a perspective viewof the FinFET 200 including a first dielectric layer 214, which isformed over the semiconductor substrate 202, the fin 212, the pad layer204, and the first mask layer 206 at one of the various stages offabrication, according to some embodiments, and FIG. 4B is across-sectional view of the FinFET 200 taken along line a-a (along the Xdirection) of FIG. 4A. As shown, the first dielectric layer 214 isformed over the whole FinFET 200 such that the entire trenches 213 arefilled by the material of the first dielectric layer 214, for example,silicon oxide.

In an embodiment, the first dielectric layer 214 may be deposited overthe substrate 202 using a high-density-plasma (HDP) CVD process withreacting precursors, e.g., silane (SiH₄) and oxygen (O₂). In anotherembodiment, the first dielectric layer 214 may be deposited over thesubstrate 202 using a sub-atmospheric CVD (SACVD) process or a highaspect-ratio process (HARP), wherein process gases used in suchprocesses may comprise tetraethylorthosilicate (TEOS) and ozone (O₃). Inyet another embodiment, the first dielectric layer 214 may be depositedover the substrate 202 using a spin-on-dielectric (SOD) process such as,for example, hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ),or the like.

Corresponding to operation 108 of FIG. 1A, FIG. 5A is a perspective viewof the FinFET 200 including a top surface 215 of the fin 212 beingexposed at one of the various stages of fabrication, according to someembodiments, and FIG. 5B is a cross-sectional view of the FinFET 200taken along line a-a (along the X direction) of FIG. 5A. In someembodiments, the top surface 215 is exposed by performing a polishingprocess (e.g., a chemical-mechanical polishing process) on thedielectric layer 214 (FIGS. 4A and 4B) until the first mask layer 206 isagain exposed. The first mask layer 206 and the pad layer 204 are thenremoved to expose the top surface 215.

In some embodiments, when the first mask layer 206 is formed of siliconnitride, the first mask layer 206 may be removed using a wet processusing hot phosphoric acid (H₃PO₄), and when the pad layer 204 is formedof silicon oxide, the pad layer 204 may be removed using dilutedhydrofluoric acid (HF). In some alternative embodiments, the removal ofthe first mask layer 206 and the pad layer 204 may be performed after arecession process performed on the dielectric layer 214, which will bediscussed in FIGS. 6A and 6B as follows.

Corresponding to operation 110 of FIG. 1A, FIG. 6A is a perspective viewof the FinFET 200 including an upper fin 218 of the fin 212 beingexposed at one of the various stages of fabrication, according to someembodiments, and FIG. 6B is a cross-sectional view of the FinFET 200taken along line a-a (along the X direction) of FIG. 6A. As shown,isolation features 220 are respectively formed at a lower portion of thefin 212 so as to expose the upper fin 218. In some embodiments, afterthe upper fin 218 is exposed, sidewalls 219 of the upper fin 218 areexposed together with the respective top surface 215.

In some embodiments, the isolation feature 220 may be formed byperforming at least one etching process to recess an upper portion ofthe dielectric layer 214 (FIGS. 5A and 5B). In an embodiment, theetching process may include performing a wet etching process such as,for example, dipping the substrate 202 in a hydrofluoric acid (HF)solution to recess the upper portion of the dielectric layer 214 untilthe upper fin 218 is exposed. In another embodiment, the etching processmay include performing a dry etching process such as, for example, usingetching gases fluoroform (CHF₃) and/or boron trifluoride (BF₃) to recessthe upper portion of the dielectric layer 214 until the upper fin 218 isexposed. In some embodiments, the isolation feature 220 may be referredto as a shallow trench isolation (STI).

Corresponding to operation 112 of FIG. 1A, FIG. 7A is a perspective viewof the FinFET 200 including an oxide layer 222 overlaying the upper fin218, which is formed at one of the various stages of fabrication,according to some embodiments, and FIG. 7B is a cross-sectional view ofthe FinFET 200 taken along line a-a (along the X direction) of FIG. 7A.As shown, the oxide layer 222 is formed to extend along the sidewalls219 and overlay the top surface 215 of the upper fin 218. In someembodiments, the oxide layer 220 may be formed by using a thermaloxidation process, an atomic layer deposition (ALD) process, a chemicalvapor deposition (CVD) process, or the like. In the embodiments in whichthe upper fin 218 is formed of silicon, the oxide layer 220 may includesilicon oxide. In some embodiments, the oxide layer 222 has asubstantially thin thickness (e.g., 1 nanometers (nm) to 5 nm), whichmay be removed in a subsequent operation when the FinFET 200 is intendedto being used for a certain application, e.g., a core device.

Corresponding to operation 114 of FIG. 1A, FIG. 8A is a perspective viewof the FinFET 200 including a dummy gate stack 230, which is formed atone of the various stages of fabrication, according to some embodiments,and FIG. 8B is a cross-sectional view of the FinFET 200 taken along linea-a of FIG. 8A. As shown, the dummy gate stack 230 is formed to overlaya central portion of the upper fin 218 with a corresponding centralportion of the oxide layer 222 being sandwiched therebetween.

In some embodiments, the central portion of the upper fin 218, overlaidby the dummy gate stack 230, may serve as a conduction channel (alongthe Y direction) of the FinFET 200, and the central portions of theoxide layer 222 and the protection layer 224 disposed between such theconduction channel and the dummy gate stack 230 may together serve asthe gate dielectric layer of the FinFET 200. In some alternativeembodiments, the central portions of the oxide layer 222 and theprotection layer 224 may be replaced by a high-k dielectric layer, whichis used to serve as the gate dielectric layer of the FinFET 200.

The dummy gate stack 230 includes a dummy gate electrode 232, which willbe removed in a later removal process, and spacer layers 234 extendingalong sidewalls of the dummy gate electrode 232. In some embodiments,the dummy gate electrode 232 may comprise a polysilicon material.Further, the dummy gate electrode 232 may be a polysilicon materialdoped with a uniform or non-uniform doping concentration. The dummy gateelectrode 232 may be formed using a suitable process such as ALD, CVD,physical vapor deposition (PVD), plating, or combinations thereof.

In some embodiments, the spacer layer 234 may include silicon oxide(SiO), silicon nitride (SiN), silicon oxynitride (SiON), or othersuitable material. The spacer layer 234 may comprise a single layer ormultilayer structure. In some embodiments, the spacer layer 234 may beformed by depositing a blanket layer of the spacer layer 234 by CVD,PVD, ALD, or other suitable technique, and performing an anisotropicetching process on the blanket layer to form the pair of the spacerlayer 234 along the sidewalls of the gate electrode 232, as shown in theillustrated embodiment of FIG. 8A.

Corresponding to operation 116 of FIG. 1A, FIG. 9A is a perspective viewof the FinFET 200 including source/drain (S/D) features 236, which areformed on side portions of the fin 212 that are not covered by the dummygate stack 230 at one of the various stages of fabrication c, accordingto some embodiments, and FIG. 9B is a cross-sectional view of the FinFET200 taken along line a-a of FIG. 9A. It is noted the line a-a of FIG. 9Ais not taken across the dummy gate stack 230, but across the S/Dfeatures 236. In some embodiments, the respective side portions of theoxide layer 222, and at least part of the upper fin 218 are removedbefore the formation of the S/D features 236, so that the removed sideportions of the oxide layer 220, and the upper fin 218 are shown indotted lines, respectively, in FIG. 9A. The formation of the S/D feature236 will be briefly described as follows.

In some embodiments, the side portions of the oxide layer 220 notcovered by the gate stack 230 are removed by one or more selectivewet/dry etching processes, and the side portions of the upper fin 218are removed by one or more other selective wet/dry etching processes soas to form respective recesses 237 on the sides of the dummy gate stack230. In some embodiments, each recess 237 has a bottom surface 238. Sucha recess 237 may be extended downwardly beneath a top surface 239 of theisolation feature 220, i.e., the bottom surface 238 is vertically lowerthan the top surface 239. Subsequently, the S/D features 236 areepitaxially grown from the fin 212 by using a low-pressure chemicalvapor deposition (LPCVD) process and/or a metal-organic chemical vapordeposition (MOCVD) process.

Corresponding to operation 118 of FIG. 1A, FIG. 10A is a perspectiveview of the FinFET 200 including a second dielectric layer 240, which isformed to overlay the S/D feature 236 at one of the various stages offabrication, according to some embodiments, and FIG. 10B is across-sectional view of the FinFET 200 taken along line a-a of FIG. 10A.It is noted the line a-a of FIG. 10A is not taken across the dummy gatestack 230, but across the S/D features 236.

According to some embodiments, the second dielectric layer 240 is formedto overlay the S/D feature 236 so as to protect the S/D features 236during a subsequent process, e.g., removing the dummy gate stack 230,which will be discussed below. Such a second dielectric layer 240 mayinclude a material that is selected from at least one of: silicon oxide,a low dielectric constant (low-k) material, or a combination thereof.The low-k material may include fluorinated silica glass (FSG),phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), carbondoped silicon oxide (SiO_(x)C_(y)), Black Diamond® (Applied Materials ofSanta Clara, Calif.), Xerogel, Aerogel, amorphous fluorinated carbon,Parylene, BCB (bis-benzocyclobutenes), SiLK (Dow Chemical, Midland,Mich.), polyimide, and/or other future developed low-k dielectricmaterials.

Corresponding to operation 120 of FIG. 1A, FIG. 11A is a perspectiveview of the FinFET 200 in which the dummy gate electrode 232 is removedat one of the various stages of fabrication, according to someembodiments, and FIG. 11B is a cross-sectional view of the FinFET 200taken along line a-a of FIG. 11A. For purposes of illustration, theremoved dummy gate electrode 232 is shown in dotted line. As better seenin the cross-sectional view of the FinFET 200 of FIG. 11B, after thedummy gate electrode 232 is removed, and the oxide layer 222 isoptionally removed, the central portion of the upper fin 218 (that wasoverlaid by the dummy gate electrode 232) is exposed.

In some embodiments, concurrently with or subsequently to the dummy gateelectrode 232 being removed, the spacer layer 234 may remain intact. Inthe example in which the dummy gate electrode 232 includes a polysiliconmaterial, the dummy gate electrode 232 may be removed (etched) by one ormore selective dry and/or wet etching processes until the centralportion of the protection layer 224 that was covered by the dummy gateelectrode 232 is exposed. More specifically, in some embodiments, thewet etching process includes using diluted hydrofluoric acid (DHF),and/or an amine derivative etchant (e.g., NH₄OH, NH₃(CH₃)OH, TetraMethylAmmonium Hydroxide (TMAH), etc.); and the dry etching process includesusing a plasma of reactive gas that is selected from: fluorocarbons,oxygen, chlorine, boron trichloride, nitrogen, argon, helium, or acombination thereof.

As described above, the oxide layer 222 may be optionally removed. Inthe illustrated embodiment of FIGS. 11A and 11B (and the followingfigures), after the dummy gate electrode 232 is removed, the oxide layer222 is subsequently removed by one or more selective wet etchingprocesses until the central portion of the upper fin 218 that wascovered by the dummy gate electrode 232 and the oxide layer 222 isexposed. More specifically, in some embodiments, the wet etching processto remove the oxide layer 222 includes using diluted hydrofluoric acid(DHF), and/or an amine derivative etchant (e.g., NH₄OH, NH₃(CH₃)OH,TetraMethyl Ammonium Hydroxide (TMAH), etc.

Corresponding to operation 124 of FIG. 1B, FIG. 12A is a perspectiveview of the FinFET 200 including a gate feature 250, which is formed atone of the various stages of fabrication, according to some embodiments,and FIG. 12B is a cross-sectional view of the FinFET 200 taken alongline a-a of FIG. 12A. In some embodiments, the gate feature 250,including a gate dielectric layer 252 and a conductive gate electrode254, overlays the central portion of the upper fin 218.

In some embodiments, the gate dielectric layer 252 may include a high-kdielectric material. Such a high-k dielectric material includes oxidesof Li, Be, Mg, Ca, Sr, Sc, Y, Zr, Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof. In some embodiments,the high-k dielectric material is deposited to overlay the centralportion of the upper fin 218 by CVD, PVD, ALD, or the like.

In some embodiments, the conductive gate electrode 254 may include ametal material such as, for example, Al, Cu, W, Ti, Ta, TiN, TiAl,TiAlN, TaN, NiSi, CoSi, or combinations thereof. In some alternativeembodiments, the conductive gate electrode 254 may include a polysiliconmaterial, wherein the polysilicon material may be doped with a uniformor non-uniform doping concentration. The conductive gate electrode 254may be formed using a suitable process such as ALD, CVD, PVD, plating,or combinations thereof. Although the conductive gate electrode 254 isshown as a single layer in the illustrated embodiments of FIGS. 12A and12B, it is understood that the conductive gate electrode 254 may includeplural above-described metal materials stacked on top to one another.

Corresponding to operation 126 of FIG. 1B, FIG. 13A is a perspectiveview of the FinFET 200 including a third dielectric layer 260 overlayingthe gate stack 250 and the second dielectric layer 240, which is formedat one of the various stages of fabrication, according to someembodiments, and FIG. 13B is a cross-sectional view of the FinFET 200taken along line a-a of FIG. 13A. In some embodiments, the thirddielectric layer 260 may be referred to as an inter-layer dielectric(ILD) layer.

According to some embodiments, the third dielectric layer 260 is formedto be partially recessed so as to re-expose respective top surface ofthe S/D features 236 and the gate electrode 254, which will be discussedbelow. In some embodiments, such a third dielectric layer 260 may beformed of a material substantially similar to the material of the seconddielectric layer 240. For example, the third dielectric layer 260 mayinclude a material that is selected from at least one of: silicon oxide,a low dielectric constant (low-k) material, or a combination thereof.The low-k material may include fluorinated silica glass (FSG),phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), carbondoped silicon oxide (SiO_(x)C_(y)), Black Diamond® (Applied Materials ofSanta Clara, Calif.), Xerogel, Aerogel, amorphous fluorinated carbon,Parylene, BCB (bis-benzocyclobutenes), SiLK (Dow Chemical, Midland,Mich.), polyimide, and/or other future developed low-k dielectricmaterials.

Corresponding to operation 128 of FIG. 1B, FIG. 14A is a perspectiveview of the FinFET 200 in which the third dielectric layer 260 isrecessed to re-expose, at least part of, respective top surfaces of theS/D features 236 and the gate electrode 254 at one of the various stagesof fabrication, according to some embodiments, and FIGS. 14B and 14C arecross-sectional views of the FinFET 200 taken along line a-a and lineb-b of FIG. 14A, respectively.

As shown, after the third dielectric layer 260 is recessed, openings 261and 263 are respectively formed. More specifically, in some embodiments,the opening 261 re-exposes a portion of a top surface 254-1 of the gateelectrode 254, as better seen in the cross-sectional view of FIG. 14B;and the openings 263 each re-exposes a portion of a top surface 236-1 ofone of the S/D features 236, as better seen in the cross-sectional viewof FIG. 14C. Although in the illustrated embodiments of FIGS. 14A-14C,the opening 263 re-exposes only the portion of the top surface 236-1, itis noted that the opening 263 may re-expose substantially the whole topsurface 236-1 and at least part of side surfaces 236-2 and 236-2 whileremaining within the scope of the present disclosure.

In some embodiments, the openings 261 and 263 may be, concurrently orrespectively, formed using one or more dry etching processes. Morespecifically, such one or more dry etching processes include using aplasma of reactive gas that is selected from: fluorocarbons (CF₄),hydrogen bromide (HBr), chlorine (Cl₂), oxygen (O), nitrogen (N), argon(Ar), helium (He), or a combination thereof.

Corresponding to operation 130 of FIG. 1B, FIG. 15A is a perspectiveview of the FinFET 200 including contact structures 270 and 272, whichare formed at one of the various stages of fabrication, according tosome embodiments, and FIGS. 15B and 15C are cross-sectional views of theFinFET 200 taken along line a-a and line b-b of FIG. 15A, respectively.

As shown, the contact structure 270 extends through the third dielectriclayer 260 and directly contacts the portion of the top surface 254-1 ofthe gate electrode 254, as better seen in the cross-sectional view ofFIG. 15B; and the contact structures 272 each extends through the thirddielectric layer 260 and the second dielectric layer 240, and directlycontacts the portion of the top surface 236-1 of one of the S/D features236, as better seen in the cross-sectional view of FIG. 15C. In someembodiments, the contact structures 270 and 272 each includes a tungstencontact that is formed by the fluoride-free CVD technique, whicheliminates the aforementioned requirement of forming the fluoridebarrier layer prior to forming the tungsten contact. The fluoride-freeCVD technique will be discussed in further detail below. In other words,the contact structures 270 and 272 are respectively coupled to the gateelectrode 254 and S/D feature 236 without a fluoride barrier layersandwiched therebetween. As such, the issue of un-scalable fluoridebarrier layer, which typically occurs when forming exiting tungstencontacts, can be advantageously eliminated.

In some embodiments, the fluoride-free CVD technique may includeperforming at least some of the following processes: placing the FinFET200 with the recessed openings 261 and 263 (FIGS. 14A-14C) in a CVD, orMOCVD, chamber; subliming a metalorganic tungsten-containing compound toa gaseous phase as a tungsten-containing precursor (e.g., tungstenhexacarbonyl (W(CO)₆)); mixing the tungsten-containing precursor with acarrier gas (e.g., argon, helium and/or nitrogen); flowing a mixture ofthe tungsten-containing precursor and the carrier gas to the chamber,wherein a pressure of the chamber is maintained at about 0.1 Torr toabout 20 Torr and a temperature of the FinFET 200 is maintained at about200° C. to about 500° C. As such, the tungsten-containing gas may bedecomposed into a plurality of tungsten atoms to refill the recessedopenings 261 and 263 with the tungsten atoms so as to form the tungstencontacts 270 and 272. In some embodiments, the decomposition process ofthe tungsten-containing gas may be represented by the following chemicalformula: W(CO)₆+2H→W+5CO+H₂CO*, wherein the symbol * is generallyreferred to a radical form of a respective atom/molecule. In someembodiments, after refilling the recessed openings 261 and 263 with thetungsten atoms, a chemical-mechanical polishing process may be performedto polished out excessive tungsten atoms.

In an embodiment, a semiconductor device includes: a fin structuredisposed on a substrate; a gate feature that traverses the fin structureto overlay a central portion of the fin structure; a pair ofsource/drain features, along the fin structure, that are disposed atrespective sides of the gate feature; and a plurality of contactstructures that are formed of tungsten, wherein a gate electrode of thegate feature and the pair of source/drain features are each directlycoupled to a respective one of the plurality of contact structures.

In another embodiment, a semiconductor device includes: a fin structuredisposed on a substrate; a gate feature that traverses the fin structureto overlay a central portion of the fin structure; a pair ofsource/drain features, along the fin structure, that are disposed atrespective sides of the gate feature; and a plurality of contactstructures, wherein at least part of the plurality of contact structuresare formed of tungsten and each directly contacts either a top surfaceof a gate electrode of the gate feature or a respective top surface ofone of the pair of source/drain features.

Yet in another embodiment, a semiconductor device includes: a conductivefeature disposed over a substrate; a dielectric layer disposed over theconductive feature; and a tungsten contact, extending through thedielectric layer, directly contacts the conductive feature.

The foregoing outlines features of several embodiments so that thoseordinary skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

1. A semiconductor device, comprising: a fin structure disposed on asubstrate; a gate feature that traverses the fin structure to overlay acentral portion of the fin structure, wherein the gate feature islocated in a first dielectric layer; a pair of source/drain features,along the fin structure, that are disposed at respective sides of thegate feature; a first contact structure extending through a seconddielectric layer located above the first dielectric layer and directlycontacting a top surface of a gate electrode of the gate feature; asecond contact structure extending through the second dielectric layerand at least partially through the first dielectric layer to directlycontact a source feature of the pair of source/drain features; and athird contact structure extending through the second dielectric layer atleast partially through the first dielectric layer to directly contact adrain feature of the pair of source/drain features.
 2. The device ofclaim 1, wherein the first, second and third contact structures areformed by a fluoride-free chemical vapor deposition technique.
 3. Thedevice of claim 2, wherein the fluoride-free chemical vapor depositiontechnique uses a precursor of tungsten hexacarbonyl.
 4. The device ofclaim 1, wherein the gate feature further comprises a gate dielectriclayer disposed between the central portion of the fin structure and thegate electrode.
 5. The device of claim 4, wherein the gate dielectriclayer comprises a high-k dielectric layer.
 6. (canceled)
 7. The deviceof claim 1, wherein the second dielectric layer is formed of a low-kdielectric material.
 8. A semiconductor device, comprising: a finstructure disposed on a substrate, wherein the fin structure is locatedat least partially in an oxide layer; a gate feature that traverses thefin structure to overlay a central portion of the fin structure, whereinthe gate feature comprises a gate electrode and is located in a firstdielectric layer located above the oxide layer; a pair of source/drainfeatures, along the fin structure, that are disposed at respective sidesof the gate feature, the pair of source/drain features located partiallyin the first dielectric layer and partially in the oxide layer; and aplurality of contact structures extending through a second dielectriclayer located above the first dielectric layer, wherein at least part ofthe plurality of contact structures are formed of tungsten and eachdirectly contacts either a top surface of a gate electrode of the gatefeature or a respective top surface of one of the pair of source/drainfeatures.
 9. The device of claim 8, wherein the at least part of theplurality of contact structures are formed by a fluoride-free chemicalvapor deposition technique.
 10. The device of claim 9, wherein thefluoride-free chemical vapor deposition technique uses a precursor oftungsten hexacarbonyl.
 11. The device of claim 8, wherein the gatefeature further comprises a gate dielectric layer disposed between thecentral portion of the fin structure and the gate electrode.
 12. Thedevice of claim 11, wherein the gate dielectric layer comprises a high-kdielectric layer.
 13. The device of claim 8, wherein the plurality ofcontact structures each extends through at least one dielectric layerformed above the gate feature and the pair of source/drain features. 14.The device of claim 13, wherein the at least one dielectric layer isformed of a low-k dielectric material.
 15. A semiconductor device,comprising: a first conductive feature disposed over a substrate,wherein the conductive feature is located at least partially in a firstdielectric layer; a second dielectric layer disposed over the conductivefeature and the first dielectric layer; a second conductive featurelocated in the second dielectric layer; a third dielectric layerdisposed over the second dielectric layer; a first tungsten contactextending through the third dielectric layer to contact a top surface ofthe second conductive feature; and a second tungsten contact, extendingthrough the third dielectric layer and partially through the seconddielectric layer and directly contacting a top surface of the firstconductive feature.
 16. The device of claim 15, wherein the tungstencontact is formed by a fluoride-free chemical vapor depositiontechnique.
 17. The device of claim 16, wherein the fluoride-freechemical vapor deposition technique uses a precursor of tungstenhexacarbonyl.
 18. The device of claim 15, wherein the first conductivefeature comprises at least one of: a drain feature and a source featureof a metal-oxide-semiconductor field-effect-transistor.
 19. The deviceof claim 15, wherein the second dielectric layer is formed of a low-kdielectric material.
 20. (canceled)